As part of a comprehensive study of current and former US Air Force personnel, an extensive assessment of the immune system of 497 normal male subjects was conducted in 1987. Cell surface marker studies for CD2 (total T cells), CD4 (helper T cells), CD8 (suppressor T cells), CD25 (activated T cells), CD20 (total B cells), CD14 (monocytes), and HLA-DR positive cell populations were measured. The CD4/CD8 ratio was also calculated. Functional stimulation assays were also performed using phytohemagglutinin (PHA) and a culture of mixed lymphocytes. Assays of natural killer cells with and without interleukin-2 stimulation were done. In addition to the distribution and range of values for each assay, statistical analyses were performed to determine the effect of age, race, percentage body fat, tobacco use and alcohol consumption on each variable. Age and alcohol consumption had significant correlation with suppressed counts and functions on nearly all variables while tobacco use was associated with stimulation of both T-cell numbers and function. These findings highlight the importance of using age-specific ranges of normal values for these tests of immunity and the need to consider life-style factors in the interpretation of the laboratory assessment of immune status.